Traumatic brain injury (TBI) is associated with blood vessels and hemorrhage. The primary TBI injury initiates release of thrombin, oxyhemoglobin (oxyHb), cytokines, ROS), and others. These molecules mediate secondary injury through multiple pathways. Since a number of molecules and signaling pathways are implicated in the injury and behavioral deficits post- ruptured many molecules, including reactive oxygen species, blocking a single mediator or single pathway may not be as clinically effective in human TBI. This led the investigators of this proposal to consider an approach that would block multiple pathways. Src family kinases (SFKs) are non-receptor tyrosine kinases, including nine family members: c-Src, Fyn, Lyn, Yrk, Fgr, Yes, Hck, Blk and Lck. SFKs can be activated by many trans-membrane receptors, such as adhesion receptors, tyrosine kinase receptors, G protein-coupled receptors, cytokine receptors, and others. This unique feature of SFKs makes them a point of convergence for many toxic molecules (e.g. thrombin, oxyHb, ROS, cytokines, and others) that are released and mediate secondary injury after TBI. Moreover, the activated SFKs initiate many neurotoxic down-stream signaling pathways including RhoA- Rho- kinase1 (ROCK1), Jun N-terminal kinase (JNK), P38 and Erk mitogen-activated protein kinases (MAPKs). Therefore, the investigators propose that blocking SFKs may provide a novel and powerful approach for treating TBI via blocking multiple detrimental pathways in which many SFK upstream toxic molecules (e.g., thrombin, oxyHb, ROS, cytokines and others) and as well as many SFK downstream effectors (e.g. ROCK1, JNK, P38, Erk, and others) are implicated. However, studying all of these pathways is beyond the scope of a single proposal. Thus, the investigators will focus this study on a linear pathway to show proof of principle that SFKs play an important role in TBI: TBI ? bleeding ? thrombin ? SFKs ? ROCK1 ? secondary injury. The investigators hypothesize that acutely blocking SFKs and acutely blocking SFK down-stream target ROCK1 post TBI will prevent hippocampal cell loss and improve cognitive outcomes many weeks after TBI. Using a rodent moderate lateral fluid percussion (LFP) model in this proposal, the investigators have shown (1) thrombin increases in cerebrospinal fluid (CSF) and SFK activity increases after TBI , and thrombin alone causes cognitive deficits through activation of SFKs; (2) Acute inhibition of SFKs using a non-specific SFK inhibitor, PP2, or nanoparticle-based in vivo small interfering RNAs (siRNAs) to SFK subtypes (Fyn and c-Src), protects hippocampal neurons and improves cognitive function after TBI; (3) PP2 blocks ROCK1 expression after TBI, and a ROCK 1 inhibitor, Y27632, improves hippocampal neuron survival and memory function after TBI. The project has the potential to be translated to humans, since SFK antagonists have been safely given to humans, and the in vivo nanoparticle delivery methods are FDA approved for human use.